Janus Streamer

A Scalable WebRTC Media Streaming Server

This repository contains the source code for our CCNC '26 paper:

Janus Streamer: A Scalable WebRTC Media Streaming Server Jaehyeong Park, Seongyeop Jeong, Seung Min Kim, Jin-Soo Kim 2026 IEEE 23rd Consumer Communications & Networking Conference (CCNC)

Overview

Janus Streamer is an enhanced version of Janus Gateway designed to address scalability limitations in high-load streaming environments. While Janus Gateway's modular architecture separates core and plugin threads via a producer-consumer model, this design incurs significant overhead from queue manipulation, memory management, and context switching as client counts increase.

Janus Streamer introduces a direct packet transmission interface that allows plugin threads to send RTP packets directly to clients, bypassing the core event-loop. Combined with additional optimizations, Janus Streamer achieves:

• 3.6x throughput improvement (up to 90 Gbps on 40 CPU cores)
• 37% reduction in CPU usage
• 3.1x - 5.7x throughput improvement on a single CPU core (depending on bitrate)
• Comparable Quality of Experience (QoE) to baseline Janus Gateway

Key Features

Feature	Description
Direct Packet Transmission	New relay_rtps interface enables plugins to transmit RTP packets directly, eliminating queue-based overhead
sendmmsg	Batch multiple UDP packets in a single system call to reduce syscall overhead
UDP GSO (Generic Segmentation Offload)	Merge RTP packets into larger datagrams for efficient NIC-level segmentation
CPU Affinity	Pin helper threads to specific CPU cores to avoid cache-line contention

Architecture

┌─────────────────────────────────────────────────────────────────┐
│                        Janus Streamer                           │
├─────────────────────────────────────────────────────────────────┤
│  ┌─────────────────┐    ┌─────────────────────────────────────┐ │
│  │ Streaming Plugin│    │              Core                   │ │
│  │  ┌───────────┐  │    │  ┌─────────┐    ┌───────────────┐   │ │
│  │  │   Relay   │──┼────┼─>│  Queue  │───>│  Event-loop   │   │ │
│  │  │  Thread   │  │    │  └─────────┘    │    Thread     │   │ │
│  │  └───────────┘  │    │                 └───────┬───────┘   │ │
│  │  ┌───────────┐  │    │                         │           │ │
│  │  │  Helper   │──┼────┼─────────────────────────┼───────────┼─┼──> Client
│  │  │  Threads  │  │    │    Direct Transmission  │           │ │   (RTP)
│  │  └───────────┘  │    │    (New Data Plane)     v           │ │
│  └─────────────────┘    │                 ┌───────────────┐   │ │
│                         │                 │    Socket     │───┼─┼──> Client
│                         │                 └───────────────┘   │ │   (RTCP)
│                         └─────────────────────────────────────┘ │
└─────────────────────────────────────────────────────────────────┘
        ───────> RTP (Direct)        - - - -> RTCP (via Event-loop)

Repository Structure

janus-streamer/
├── src/
│   ├── janus.c/h          # Core server implementation
│   ├── ice.c/h            # ICE/DTLS/WebRTC handling (modified for GSO/sendmmsg)
│   ├── plugins/
│   │   ├── janus_streaming.c   # Streaming plugin (modified for direct transmission)
│   │   └── ...
│   ├── transports/        # Transport plugins (HTTP, WebSocket, etc.)
│   └── events/            # Event handler plugins
├── conf/                  # Configuration file samples
├── test/                  # Test scripts (aiortc-based)
└── html/                  # Web demo files

System Requirements

Hardware (Tested Environment)

• 1-socket x86_64 CPU (40 cores, Intel Xeon Gold 5218R)
• Mellanox ConnectX-5 100GbE NIC

Software

• Linux kernel version: 5.4.0 or later (for UDP GSO and sendmmsg support)